Electromechanical brakes are known that comprise a stack of disks and at least one actuator which comprises a pusher and an electric motor arranged to move the pusher in register with the stack of disks so as to press the pusher against the stack.
The electric motor is controlled to press the pusher against the stack of disks with pressure that is equal to a nominal pressure that is a function of the desired braking intensity, which nominal pressure may be modulated in response to detecting slip of the wheels braked in this way, so as to prevent said wheels from locking.
The electric motor must therefore be dimensioned to perform the following functions:                a rapid approach of the pusher towards the stack of disks, under negligible torque;        the application of nominal pressure to the stack of disks, at a controlled speed that is generally slow but under high torque; and        modulating the nominal pressure, which requires displacements to be performed that are short but very rapid, and under high torque.        
The third condition is very constraining and requires powerful motors to be used, and thus motors that are heavy and that present the drawback of large inertia.
Proposals have been made, for example in document DE 198 58 764 A, to place a piezoelectric assembly in the pusher of the actuator, the piezoelectric assembly serving to modulate the nominal pressure, while the electric motor is used solely to apply the nominal pressure, thus making it possible to use electric motors of lower power, that are thus lighter in weight, and that consume less electricity.
Nevertheless, in the configuration proposed in that document, the piezoelectric assembly moves with the pusher, thereby complicating the provision of electrical connections to the piezoelectric assembly.
The state of the art is also illustrated by the following documents U.S. Pat. No. 5,090,518 A, U.S. Pat. No. 6,179,097 A, or indeed EP 0 984 190 A.